1. Field of the Invention
The present invention relates generally to prosthetic vascular grafts for implantation within the vascular system of a patient, and more particularly, to a prosthetic vascular graft made from expanded, porous polytetrafluorethylene (PTFE) tubing that is fabricated to be longitudinally compliant for allowing at least a portion of the PTFE graft to be stretched along the longitudinal axis thereof.
2. Description of the Prior Art
The use of implantable prosthetic vascular grafts made of expanded, porous PTFE is well known in the art. Such vascular grafts are often implanted just below the skin to provide blood access for long term hemodialysis. Such PTFE vascular grafts are also used to replace or bypass occluded or damaged natural blood vessels. Such prosthetic vascular grafts, and methods of implanting the same, are generally described in Bennion et al., "Hemodialysis and Vascular Access", Vascular Surgery. pp. 625-662, 1983. Methods of forming expanded, porous PTFE tubing are well known in the art. For example, U.S. Pat. No. 4,187,390 issued to Gore discloses one such process which may be used to produce highly porous, expanded PTFE structures.
Expanded, porous PTFE material offers a number of advantages when used as a prosthetic vascular graft. PTFE is highly biocompatible, has excellent mechanical and handling characteristics does not require preclotting with the patient's blood, heals relatively quickly following implantation, and is thromboresistent. Notwithstanding its many advantages, certain problems may arise with the use of PTFE vascular grafts. For example, PTFE material is not very elastic, and the suture holes formed in the ends of the graft when the graft is sutured to a blood vessel during implantation often leak blood until clotting occurs Within the suture holes. Moreover, in those instances when a PTFE vascular graft is implanted below the skin for being cannulated by a hemodialysis needle, the vascular graft must be tunneled under the skin between the artery and vein to which the graft is to be anastomosed. Occasionally, a surgeon will misjudge the length of the graft that is required to reach between the selected artery and vein; in these situations, the surgeon may find that the graft is too short to reach the targeted site once the graft has been tunnelled under the skin. PTFE vascular grafts typically exhibit minimal longitudinal compliance, and hence the graft may not be stretched significantly along its longitudinal axis. Accordingly, in such cases, the surgeon must then remove the tunnelled graft from below the skin and repeat the tunneling procedure with a longer graft.
As mentioned above, PTFE vascular grafts are often used to provide a bypass within the vascular system. Two examples of the use of PTFE vascular grafts as bypass implants include an axillofemoral bypass graft, wherein the vascular graft extends between the femoral artery in the upper leg to the axillary artery in the shoulder, as well as a femoropopliteal bypass graft extending below the knee. Such bypass grafts often place restrictions upon the freedom of movement of the patient in order to avoid pulling the graft loose from its anchor points. For example, in the case of the axillofemoral bypass graft, sudden or extreme movements of the arm or shoulder must be entirely avoided. Similarly, in the case of the femoropopliteal bypass graft, bending the knee can place dangerous stress upon the graft. The above-described restricted movement is due largely to the inability of the PTFE vascular graft to stretch along its longitudinal axis when its associated anchor points are pulled apart from one another. Such restrictive movement is especially important during the early period of healing following implantation When there is still little tissue incorporation into the graft and it can move within the subcutaneous tunnel.
Furthermore, some medical studies have suggested that vascular graft compliance may play an important role in graft failure. These studies make note of the mechanical mismatch created by surgical anastomoses, due in part to the inability of PTFE vascular grafts to exhibit any longitudinal or radial compliance. In this regard, see generally Shu et al., "Flow Phenomena In Compliant And Noncompliant Arteriovenous Grafts", Trans Am Soc. Artif. Intern. Organs, vol. XXXIV, 1988, pp. 519-523; and Kenney et al., "Evaluation of Compliant And Noncompliant PTFE Vascular Prostheses", Trans Am Soc. Artif. Intern. Organs, vol. XXXIV, 1988, pp. 661-663.
Accordingly, it is an object of the present invention to provide a PTFE prosthetic vascular graft which retains the advantages of using PTFE material as described above, but which is longitudinally compliant over at least a portion of its length for allowing the graft to be stretched along its longitudinal axis
It is another object of the present invention to provide such a longitudinally compliant PTFE graft which minimizes suture hole bleeding at the ends of the graft at those points where the graft is anastomosed to blood vessels within the body.
It is still another object of the present invention to provide such a vascular graft which may be stretched along its longitudinal axis, and thereby make less critical the sizing of the graft prior to implantation.
It is a further object of the present invention to provide such a longitudinally compliant vascular graft which permits a patient greater freedom of movement and which minimizes the likelihood of the ends of the graft pulling loose from their associated anchor points when the graft is stretched due to movements of the patient's body.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.